Process for the manufacture of paper and paperboard

Abstract

The present invention relates to a process of making paper or paperboard in which a cellulosic thin stock is provided and subjected to one or more shear stages and then drained and a moving screen to form a sheet which is dried, wherein the process employs a retention system which is applied to the thin stock, said retention system comprising as components i) a blend of different cationic polymers and ii) a microparticulate material, in which the blend of cationic polymers comprises, a) a cationic polymer having a charge density of at least 3 mEq per gram and a molar mass of greater than 700,000 Da, b) a cationic polymer having a charge density of below 3 mEq per gram and an intrinsic viscosity of at least 3 dl / g, wherein one of the components of the retention system is dosed into the thin stock after the final shearing stage and the other is dosed into the thin stock before the final shearing stage.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present application is a 35 U.S.C. §371 national stage patent application of International patent application PCT / EP2013 / 051921, filed on Jan. 31, 2013, published as WO / 2013 / 113823 on Aug. 8, 2013, the text of which is incorporated by reference, and claims the benefit of the filing date of application no. PCT / CN2012 / 070821, filed on Feb. 1, 2012, the text of which is also incorporated by reference.BACKGROUND OF THE INVENTION[0002](1) Field of the Invention[0003]The present invention relates to a method for the manufacture of paper and paperboard from a cellulosic suspension, employing a novel retention system.[0004](2) Description of the Background Art[0005]It is well known to manufacture paper by a process that comprises flocculating a cellulosic thin stock by the addition of polymeric retention aid and then draining the flocculated suspension through a moving screen (often referred to as a machine wire) and then forming a wet sheet,...

AI Technical Summary

Benefits of technology

The present invention is a process that increases the speed of machines, especially when making board, while improving retention without necessarily increasing drainage. The process also allows for better runnability, with sheets of paper and board produced exhibiting improved formation and strength. This process also increases productivity of paper and board.

Problems solved by technology

However, it is known that increasing the molecular weight of a polymeric retention aid which is added immediately prior to drainage will tend to increase the rate of drainage but damage formation.

It is difficult to obtain the optimum balance of retention, drainage, drying and formation by adding a single polymeric retention aid and it is therefore common practice to add two separate materials in sequence.

However, this process can sometimes suffer the disadvantage when making fine paper of a yellowing tendency.

A particular disadvantage of many conventional microparticle systems is that drainage tends to increase simultaneously with increasing retention.

Although this may have been perceived as an advantage several years ago, with modern high-speed paper machines very high drainage can be a disadvantage.

Nevertheless in most cases it is necessary to reduce the paper machine speed for the higher basis weight sheets because of these drainage limitations.

Further, formation can also be adversely affected.